An uncalibrated pulse contour method to measure cardiac output during aortic counterpulsation.

BACKGROUND: Less-invasive monitoring systems, such as pulse contour methods, are increasingly being used to estimate cardiac output (CO). However, alterations in the arterial waveform caused by intraaortic balloon pump counterpulsation may affect the ability of pulse contour algorithms to determine CO. We investigated the reliability of an uncalibrated pulse contour method, the MostCare system, in patients with cardiac failure receiving intraaortic balloon pump counterpulsation by comparing its measurements of CO with those determined by an intermittent thermodilution method.

METHODS: The study included 15 patients requiring hemodynamic support with an intraaortic balloon pump after coronary artery bypass graft surgery. A pulmonary artery catheter was inserted and CO was determined by bolus thermodilution (ThD-CO). The MostCare device was directly connected to the standard monitoring system for analysis of the radial artery pressure wave and computation of CO (MostCare-CO). Data were collected at 3 different intraaortic balloon pump rates (1:1, 1:2, 1:4) and after intraaortic balloon pump removal.

RESULTS: One hundred six pairs of ThD-CO and MostCare-CO measurements were analyzed. There was a good correlation between ThD-CO and MostCare-CO (r = 0.90, 95% confidence interval [CI] = 0.86-0.93; P < 0.001). The mean bias of all CO measurements corrected for repeated measures was -0.2 L/min with limits of agreements of -1.31 to 0.91 L/min (lower 95% CI, -1.72 to -0.90; upper 95% CI, 0.50-1.32) and a relative percentage error of 24. There were close agreements between ThD-CO and MostCare-CO at the different intraaortic balloon pump rate settings. Changes in CO were calculated separately for the 2 methods and data comparison showed a correlation of 0.82 (95% CI = 0.76-0.87; P < 0.001) and a mean bias of 0.14 L/min with limits of agreement of -1.31 to 1.59 L/min (lower 95% CI, -1.62 to -1.00; upper 95% CI, 1.28-1.90).

CONCLUSION: The MostCare system provided measurements of CO that were comparable to ThD-CO in patients assisted with an intraaortic balloon pump. The reliability of the MostCare system is not significantly affected by changes in arterial waveform morphology caused by inflation and deflation of the intraaortic balloon pump.